This invention relates to a device for measuring the axial and tangential forces exerted on a spool of fiber optic datalink filament as the filament is drawn off of the spool at predetermined rates. The spool of datalink filament is adapted to be carried by a guided missile and paid out as the missile flies from its launching point to a target. The fiber optic datalink filament connects the missile to a guide and ground control mechanism at the launch site. A description of a typical missile utilizing the fiber optics for guidance purposes is found is U.S. Pat. No. 4,185,796.
When preparing spools of datalink filament for use in such missiles it is important to prepare the spool with the proper degree of resistance to sloughing off the spool during flight while at the same time permitting paying out of the filament during the flight of the missile. Since it is difficult to measure the forces exerted on the filament and the spool during the flight of the missile itself it has been proposed to measure these forces on a ground test apparatus as the filament is withdrawn from the spool at speeds comparable to those exerted on it during the flight of the missile itself.
It has been recognized that a force and torque sensing spool fixture is required to measure the forces of interest imparted to the spool during flight. A previous system has been developed by Hughes Aircraft to solve this problem. The Hughes system addressed this problem by supporting the spool by means of a bushing or bearing to isolate the loads due to the weight of the spool itself. Force transducers of various types were then attached to the support shaft of the spool to measure the forces of interest. A problem with the Hughes Aircraft system was that the desired signal levels are so small that they were swamped by hysteresis in the measurement system, due to friction in the supporting members bushings, bearings and the like. This rendered the fixture of Hughes inadequate for measuring the forces of interest.
Another system, developed by Optelecom, Inc., supported the spool on a shaft which, in turn, was suspended by air bearings. Data is not available on the success of this system but the added complexity of air bearings makes the system inconvenient to use in the laboratory.